Using a pair of polarizing sunglasses, you can demonstrate the effects of polarization together with a computer screen which is also polarizing. When the axes of polarization of the two polarizing screens are rotated, the brightness alternates between bright and dark.
Light coming from a computer screen is usually polarized. In the video below, when polarized light passes through another polarizer, the intensity of the light is given by Malus' law:
where is the angle between the two axes of polarization and is the original intensity of the unpolarized light.
Only the components of electric field vectors in electromagnetic radiation that are parallel to the axis of polarization of a polarizing filter will be permitted through. Those electric field components that are perpendicular to the polarization axis are blocked by the filter.
Hence, the amplitude of a vector A that passes through is given by . Since intensity is proportional to the square of amplitude (), we have Malus' law.
The purpose of having polarizing filters in sunglasses and computer screens is to cut out glare due to light from other sources.